The present invention is related to permanent magnet generators, and in particular to permanent magnet generators that provide protection from short-circuit conditions.
Permanent magnet generators (PMGs) are a special type of generator that relies on permanent magnets to generate the magnetic field(s) necessary to operate the generator. This is in contrast with other types of generators, which typically employ an excitation current to generate the desired magnetic field. While PMGs outperform more traditional motors and generators in many applications, one of the benefits of more traditional systems is the ability to quickly remove excitation and therefore the presence of the magnetic field in the event of a fault condition. Because the magnetic field in PMGs is generated by permanent magnets, there is no mechanism for shutting down the machine quickly in the event of a fault. For example, in response to a short-circuit condition in a permanent magnet generator (PMG), the generator will continue providing a voltage until the rotating portion of the generator comes to rest. During this time the short-circuit fault may cause considerable damage to the PMG.